Greenhouses are typically used to provide a controlled environment for plant growth. The environment within a greenhouse is controlled by varying the amount of sunlight, heat and ventilation. Various structures of greenhouses exist in the art to provide plant growth in a controlled environment. These structures vary in complexity and consist of both fixed and portable embodiments.
A typical greenhouse consists of a framework enclosing a space; this framework being covered with a flexible material such that plants in the enclosed space can be provided with varying amounts of light and ventilation through various techniques of adjusting the flexible material.
One such technique is disclosed in U.S. Pat. No. 5,038,517 issued Aug. 13, 1991 to Talbott and describes a greenhouse with a flexible cover positionable over the frame for providing a roof enclosure for the structure. An elongate roller is secured to a lengthwise edge of the cover and a power source is coupled to the roller. When the roller is rotated about its longitudinal axis with the help of the power source, the cover retracts or extends relative to the frame thereby providing the plants with variable amounts of light and ventilation.
U.S. Pat. No. 5,216,834 issued Jun. 8, 1993 to Crowley provides another technique that utilizes a pair of opposed spools mounted on respective sides of a framework such that the cover is wound from one spool to the opposed spool.
U.S. Pat. No. 5,813,169 issued Sep. 29, 1998 to Engerman discloses a portable greenhouse construction with a roof that is arch shaped and includes a pair of retractable, translucent covers which are rolled up onto a shaft to permit fresh air into the interior of the greenhouse through a mesh screen.
Prior art methods of adjusting flexible covers for greenhouses pose several significant problems. First, present systems allow for retraction of flexible covers in only one direction, from down up, and extension also in one direction, from up down. Therefore effective control of sunlight falling on the plants can only be accomplished partially with prior art greenhouse embodiments. Adjusting openings in a greenhouse roof based on wind direction is also limited.
Another problem with current apparatus is the need for a rotatable shaft attachment for extension or retraction of the flexible covers. The use of this increases the complexity and also the time taken to assemble the system by adding a step to the process.
An offshoot of increased structural complexity of the greenhouse is increased cost and also more difficulty in installing additional sections to increase the length of the greenhouse.
Therefore, a means for bi-directional extension and retraction of covers for greenhouses which simultaneously eliminates the need for an attached rotatable shaft to accomplish cover adjustment is desired. Reduced structural complexity, decreased cost and ease of adding additional sections are also desired.